docs: def writefits(self,fname,clobber=True, trimzero=True, binned=True,
                    hkeys=None):
          """Like :meth:`pysynphot.spectrum.SourceSpectrum.writefits`
          but with ``binned=True`` as default.
  
          """
          spectrum.CompositeSourceSpectrum.writefits(self,fname,
                                                     clobber=clobber,
                                                     trimzero=trimzero,
                                                     binned=binned,
                                                     hkeys=hkeys)